1. Field of the Invention
The present invention relates to technology of a reserve tank used in a cooling system for cooling an object to be cooled.
2. Description of the Related Art
Auxiliary machines such as engines, motor generators, inverters, air compressors, and air-conditioning units provided on vehicles such as hybrid cars and electric cars generate heat at the time of driving. Vehicles such as hybrid cars and electric cars are provided with a cooling system for cooling with coolant to maintain proper temperature of heat-generating auxiliary machines (objects to be cooled).
FIG. 5 is a schematic diagram of a configuration of a typical cooling system. As shown in FIG. 5, a cooling system 2 includes a pump 58 that circulates coolant water, an inverter 60 (object to be cooled), a radiator 62 as a heat exchanger that causes heat exchange between the coolant water and ambient air, a reserve tank 64, and circulating paths 66a, 66b, 66c, and 66d. 
Although the cooling system will be described in detail later, the pump 58 is operated to cause the heat exchange between the coolant water circulating the circulating paths 66a, 66b, 66c, and 66d (flow of the coolant water is represented by arrows shown in FIG. 5) and the inverter 60, to cool the inverter 60, which is the object to be cooled.
When the above cooling system 2 is operated, gas may mix into the coolant. Mixing the gas into the coolant causes deterioration of the heat exchange rate of the cooling system (substantially, the radiator 62) and abnormal noise and damage of the pump 58. Therefore, the reserve tank 64 having a gas-liquid separating ability is conventionally used to separate the gas in the coolant.
FIG. 6 is a schematic cross-section side view of a configuration of a typical reserve tank. As shown in FIG. 6, the reserve tank 64 has a tank main body 70, an entry tube 72, an exit tube 74, and a pressurizing cap 76 that adjusts the air pressure within the tank main body 70. The tank main body 70 has a plurality of chambers partitioned by a partition wall 78 and has a first chamber 82 provided with an inflow port 80 that allows the coolant to flow into the tank main body 70 and a second chamber 86 provided with an outflow port 84 that allows the coolant to flow out of the tank main body 70. A communicating portion 88 allowing the coolant to flow into the second chamber 86 is formed in the first chamber 82. The communicating portion 88 is a through-hole formed in the partition wall 78. The gas in the coolant may be separated when the inflow coolant from the inflow port 80 passes through the communicating portion 88.
For example, Japanese Patent Application Laid-Open Publication No. 2005-120906 proposes a reserve tank provided with an eddy suppressing means that constrains the occurrence of eddies in the coolant at the rear face of a partition wall adjacent to a through-hole formed in the partition wall to improve the air-liquid separating performance of the reserve tank.
For example, Japanese Patent Application Laid-Open Publication No. 2004-301084 proposes a reserve tank provided with a partition wall that partitions the inside of the tank into the inflow port side and the outflow port side within a height range at a position lower than the inflow port and higher than the upper end of the outflow port, and the partition wall is provided with a flow path that communicates the inflow port side and the outflow port side at a height including at least the upper end of the outflow port or higher, to improve the air-liquid separating performance of the reserve tank.
Recently, since the generated heat temperature of the object to be cooled is increased due to the higher power output of the object to be cooled (such as an inverter), a flow rate of coolant must be increased in the cooling system. Cooling systems increasingly employ an electric pump having excellent performance aspect (performance, controllability, and quietness) compared to conventional mechanical pumps. Therefore, a large amount of gas may mix into the coolant at the time of operation of the cooling system.
A liquid level (liquid level 90 shown in FIG. 6) of the coolant in the reserve tank may be tilted due to a traveling condition such as rapid start or sudden stop of a vehicle and a road surface condition such as an ascending road or a descending road. On this occasion, if the liquid level of the coolant becomes lower than the inflow port, etc., in the reserve tank, the inflow port, etc., present in the coolant are exposed to the air and the gas may mix into the coolant.